The present invention relates to a method for molding metals using high fluid pressure. As used herein, "fluid pressure" can include that of oil pressure, water pressure, or the like. "Method for molding" is used to indicate that fluid pressure is applied to a raw material to perform a molding of same into article shape.
Conventionally, articles having complex shapes including gears and the like have been molded using a female/male mold unit, i.e., a die and an punch. An example of this is described in Japanese laid-open patent publication number 5-154598.
In Japanese laid-open patent publication number 5-154598, a metal raw material is placed in a die. A punch is used to perform molding. In the molding operation, the punch and the metal raw material come into contact under high pressure so that resistance is generated between the two. This resulted in the fluidity of the metal material not always being adequately matched with the shape of the cavity.
This problem is not restricted to the molding operation disclosed in Japanese laid-open patent publication number 5-154598. It applies to all similar types of molding that use a die and a punch.
Japanese laid-open patent publication number 10-175028 and Japanese laid-open patent publication number 10-296347 are examples of conventional technology in which molding is performed using fluid pressure. In the former, a hydroform method involves a metal pipe, e.g., a copper pipe, placed in a split mold. An internal pressure, applied to the pipe, in the direction of the axis of the pipe, molds the pipe into a predetermined shape to form an article in the form of a bellows-pipe. In the latter publication, a fluid-pressure bulge processing method is presented. Internal pressure from fluid in a metal pipe is combined with axial compression of the metal pipe in order to expand a section of the metal pipe.
In both of these technologies, hollow piton-shaped members are disposed on either side of the metal pipe, which serves as the raw material. The piston-shaped members feed pressurized oil to the inner diameter of the metal pipe and push the metal pipe from both ends. These piston-shaped members are inserted into holes disposed in a split mold. The hollow section of the piston-shaped member serves as an oil passage through which the pressurized oil is fed. A sealing member is generally mounted to the outer diameter section of the piston-shaped member to prevent the fluid from leaking.
Due to its purpose, the sealing member must be flexible, so its resistance to pressure is limited. For example, such a sealing member generally cannot withstand a fluid pressure of approximately 2000 Mpa. Thus, high-pressure molding, using this method has not been conventionally possible. In both of these technologies, a high degree of process ability is provided by using the piston-shaped members to press from both ends of the raw material.